1. Field of the Invention
The present invention relates to a route guidance system and method for route guidance to a destination, to a related information delivery center, and to a vehicular route guidance apparatus. More specifically, the invention relates to a route guidance system in which a vehicular route guidance apparatus having stored road data provides a guidance display for a route to a destination while in communication with an information delivery center also having road data, as well as to such an information delivery center and vehicular route guidance apparatus.
2. Description of the Related Art
In a conventional navigation apparatus that is provided in a vehicle such as an automobile, when an operator has set a destination by operation of an input section, a route from a detected present position to the destination is searched for and route guidance is provided for the thus determined route. The route is usually determined so as to minimize the distance to be covered from the present position to the destination or to minimize the travel time.
In a conventional communication-type navigation system route guidance is performed by communication between an information center having road information and a navigation apparatus provided on a vehicle (Japanese Patent Laid-Open No. 19588/1998). In such a system, the information center reads necessary information from a database, responsive to a request from the vehicular apparatus, and generates a map image. The information center also generates information indicating an optimum route by performing a route search. The generated map image and information indicating the optimum route are sent from the information center to the vehicular apparatus and displayed on a display of the vehicular apparatus.
In such systems, the configuration of the vehicular apparatus is simplified because the vehicular apparatus need not be equipped with a database. Since the database that is maintained in the information center is updated frequently, route search results and map information that are generated based on the latest information can always be supplied to the operator.
However, because the map images and information for guidance along an optimum route are communicated from the information center to the vehicular apparatus, if the vehicle is running in an area where communication cannot be performed properly or at all, e.g., when a system is down or another problem arises in the information center, communication between the information center and the vehicular apparatus is interrupted and the vehicular apparatus cannot receive map images and information necessary for providing route guidance.
In a known navigation system that solves the problem, when communication between the information center and the vehicular apparatus cannot be performed, route guidance is continued by using map information in a storage medium such as a CD-ROM or a DVD-ROM which is provided in the vehicular apparatus (Japanese Patent Laid-Open No. 2001-147132). However, if the map information stored in the storage medium of the vehicular apparatus is old and the information center has performed a route search based on new information that is not included in that map information, route guidance that is continued by using the map information stored in the storage medium of the vehicular apparatus will be improper.
Assume a case wherein communication between the information center and the vehicular apparatus is disabled in the middle of a guidance operation for an optimum route that was found by a route search in the information center and includes a new expressway. In this case, the vehicular apparatus attempts to display a route based on the previously received information indicating the optimum route and using the map information stored in the storage medium of the vehicular apparatus. However, since the map information stored in the storage medium of the vehicular apparatus has not been updated and therefore does not include the new expressway, the vehicular apparatus cannot display a route including the new expressway on the display means. As a result, the vehicular apparatus continues the route guidance by displaying a route including another, closest road such as an ordinary road, in place of the new expressway, and the route guidance becomes improper. Further, the vehicular apparatus generates route guidance information by performing map matching and a route search using the road data etc. stored in the recording medium. As a result, the vehicular apparatus displays a vehicle present position on the substituted closest road that is recorded within the vehicular apparatus rather than on the new expressway and performs route guidance from that misplaced present position.